The invention relates to the field of the textile industry. It relates more specifically to the production of fancy fabrics used for garments or the like. It relates more particularly to improvements made to weaving processes combined with warp-yarn treatment operations. It also relates to the cloth thus obtained, which has novel patterns.
As is known, certain fancy fabrics have patterns which consist of juxtaposed warp yarns of a different nature or having different properties. When manufacturing such a fabric, it is therefore necessary for the warp yarns to come from two, or even more, different warp beams. Thus, the yarns coming from two warp beams form two parallel sheets which are mixed at the feed bars before they enter the shed-forming region. The two warp beams are needed to allow the sheets of yarns, which are either of a different nature or have undergone different pretreatments, such as dyeing, to advance differently.
Thus, the problem of managing multiple warp beams arises in several types of fancy fabric such as, in particular, cloth having a particularly novel appearance, similar to cotton crepe cloth more generally called xe2x80x9cseersuckerxe2x80x9d.
Also encountered is the problem of managing a large number of warp beams in the production of striped fabrics.
This is because, in both cases, when it is desired to combine within one and the same warp beam several types of yarns which are either of a different nature or of a different shade, this involves operations prior to weaving which are irksome or even impossible when the warp yarns to be combined are of a very different nature. Furthermore, when the various yarns are combined within one and the same warp beam, their spread and distribution are set, so that it is impossible to modify the number and width of each of the regions of specific properties.
Thus, for example, the width of the stripes is determined intangibly by the spread of the yarns of the shades used. In other words, it is necessary to have a warp beam specific to the production of each pattern. Obviously this is extremely expensive and results in the loss of time when it is desired to change patterns.
The problem is not solved when two different warp beams each comprising one type of yarn are used. This is because the mechanism allowing two yarns coming from two different warp beams to be combined, at a feed bar, into a single sheet allows only one specific type of mixing and a given and set distribution of the yarns coming from these two warp beams to occur. In other words, the looms used for producing such articles are not completely versatile but, on the contrary, are often dedicated to the production of a single type of fabric.
One of the objectives of the invention is to allow fancy fabrics chosen from a wide variety to be produced by means of a single loom which is as simple as possible and carries a single warp beam formed from a single grade of yarn.
The invention therefore relates to a process for obtaining a woven cloth. This process comprises, in a known manner, the following steps in which:
a sheet of parallel warp yarns is continuously unwound from a single warp beam;
said sheet is made to pass over a back-rest roller;
a shed is formed by means of healds, said shed being defined, in the direction of advance of the warp, at the entrance of the shed by an opening point and on the other side by a fell point;
a weft yarn is inserted into the shed in the vicinity of the fell point in order to form a cloth; and
finally, the cloth thus formed is pulled uniformly and wound up;
and in which, in the vicinity of the opening point of the shed a heating operation is carried out on the warp yarns and then said warp yarns are cooled in the shed before they reach the healds.
The process according to the present invention is characterized in that the heating operation is carried out on only a portion of the warp yarns.
In other words, the process according to the invention treats a portion of the warp yarns differentially. This means that, over the total width of the fabric, only a portion of these warp yarns undergoes the heating step which gives them specific properties.
Thus, if the heating operation is carried out on the warp yarns at a temperature high enough to cause an elongation and a local reduction in the elastic modulus, the fabric thus obtained has warp yarns which come from a single beam, delivering uniform yarns, but which are differentially converted during the weaving operation. Consequently, when the fabric obtained undergoes a subsequent shrinking step, the warp yarns behave in a different manner according to whether or not they have undergone the heat treatment during weaving. It follows that the different lengths of the warp yarns and the complementary shrinkage phenomenon cause, within the fabric, different deformations which are distributed according to the selection of the warp yarns that have or have not undergone the heating operation during weaving. This is because those yarns which have undergone the heat treatment during weaving have a lower shrinkage than those which have not been heated, and result in the appearance of embossed regions through the thickness when the unheated yarns shrink. The effects thus obtained are highly pronounced and vary according to the yarns used.
In practice, using the process according to the invention, the sheet is separated, downstream of the back-rest roller, into two series of yarns and a gap is maintained between the two series of warp yarns in order to subject only one of the two series to the characteristic heating operation. In this way, by means of two single lease rods, the sheet is divided according to the desired geometry, by selecting the number and the position of the yarns which have to be heated under tension. Thanks to the simplicity of the separating mechanism, it is possible to vary without any difficulty the distribution between the two series resulting from the sheet by selecting at will the desired distribution. For example, it may be chosen to heat only a fewer number of warp yarns, keeping a larger number of yarns unheated, which will then undergo a greater shrinkage. Conversely, it may be chosen to heat most of the warp yarns in order to obtain yet other effects.
The configuration of each of the series may also be chosen according to the wish of the user, and without any restriction, with the possibility of obtaining effects which vary over the width of the fabric. Thus, it is possible to create each series of warp yarns by using numbers of identical yarns assembled in groups or in bundles. It is also possible to vary the number of yarns per bundle over the width of the fabric, and to do so with complete freedom of choice.
In practice, the process according to the invention may advantageously furthermore include a heat treatment step xe2x80x9cin the free statexe2x80x9d. This treatment may advantageously be a scalding treatment or a hot-air treatment, without any tensile stress, such as may be obtained on continuous machines called xe2x80x9ctumblersxe2x80x9d. Thus, by forcing the shrinkage in the free state, the difference in behavior between those yarns which have undergone the heating operation and the others is accentuated, thereby causing more pronounced volume deformations. In one advantageous way of implementing the process, the shrinkage step may be followed by a calendering step, or more generally by a step in which the patterns formed are flattened, in order to give a different and flattering external appearance.
The invention also relates to the textile cloth which is obtained by means of the process according to the invention and which has an appearance similar to seersucker fabrics.
In practice, the warp yarns used may advantageously be crepe yarns and/or textured crepe yarns, that is to say crepe yarns that have undergone a twisting step and a false-twisting step. It is also possible to vary the effects within the fabric using different and lathed weft yarns.
As already stated, the cloth obtained may have extremely varied effects depending on whether the yarns which have undergone the heat treatment during weaving are in equal number or greater or lesser in number than those which have retained their shrinkability without having been heated. Furthermore, the effects may also be varied by choosing, within the series of warp yarns to be heated, bundles having either a uniform distribution or a variable distribution according to the choice of the manufacturer.
The process according to the invention may also prove to be advantageous for producing patterns on the warp yarns from a transfer paper. Thus, more specifically, according to this particular method of implementing the process:
only that portion of the warp yarns which undergoes the heating operation is brought into contact with a transfer paper carrying dye patterns, which can be transferred onto the warp yarns owing to the effect of said heating operation;
said transfer paper is made to run in a speed relationship with the speed of advance of the sheet of warp yarns, so that transfer of the dye pattern takes place only on just said portion of the warp yarns which undergoes the heating operation.
In other words, the invention consists in separating the sheet of warp yarns from the yarns intended to receive the printing in order to form bundles of yarns on which the patterns present on the transfer paper are printed, and which yarns form, when they are assembled with the other yarns of the sheet, the characteristic stripes. Consequently, only the yarns forming the stripes on the fabric are printed and the boundaries of the stripes on the fabric are perfectly well defined within one and the same yarn. The stripes are therefore perfectly straight. Yet it is known that, in conventional printing processes involving transfer from paper having stripes, the boundary between two stripes from the paper is not always located on one and the same yarn but, on the contrary, tends to move about and be distributed over several yarns, constituting a uniformity defect.
Furthermore, it has been found that, surprisingly, those yarns located at the lateral edges of stripes receive a surplus of dye during printing and have a greater intensity of color than the rest of the band. This overintensity enhances the boundary of the stripe, giving a particularly perceptible crimp effect.
In practice, when it is desired to obtain stripes of uniform width, each of the series of warp yarns is defined in such a way that they consist of bundles of yarns, each bundle having a similar number of yarns. Of course, the invention is not limited to this method of implementation alone but also allows stripes of whatever dimensions to be obtained, by selecting, in a uniform or nonuniform manner, and with complete freedom, the number of yarns which will undergo the printing step. A very wide variety can thus be obtained since it is possible to select yarn by yarn, and to obtain, in the extreme case, stripes limited to only a single yarn widthwise.
It is possible to multiply the effects, especially by selecting a transfer paper which has a pattern of parallel stripes in the direction of run of the paper, such that one of the boundaries between said bands is brought close to that portion of the warp yarns on which the printing takes place. In other words, on the same stripe obtained by selecting a portion of warp yarns, it is possible to print an additional pattern, itself consisting of stripes, these possibly moving about owing to the variation in the mixing of the two neighboring colors.
As already stated, the invention also relates to the cloth which is woven according to the invention and has a plurality of parallel stripes. As already stated, it is found that each stripe thus has a selvedge, the intensity of the shade of which is higher than the rest of the stripe.